Custom localization (#2837)

Co-authored-by: WithoutPants <53250216+WithoutPants@users.noreply.github.com>

ui/v2.5/src/docs/en/Changelog/v0170.md

@@ -5,6 +5,7 @@ After migrating, please run a scan on your entire library to populate missing da
 * Import/export schema has changed and is incompatible with the previous version.
 
 ### ✨ New Features
+* Allow overriding UI localisation strings. ([#2837](https://github.com/stashapp/stash/pull/2837))
 * Populate name from query field when creating new performer/studio/tag/gallery. ([#2701](https://github.com/stashapp/stash/pull/2701))
 * Added support for identical files. Identical files are assigned to the same scene/gallery/image and can be viewed in File Info. ([#2676](https://github.com/stashapp/stash/pull/2676))
 * Added support for filtering and sorting by file count. ([#2744](https://github.com/stashapp/stash/pull/2744))

ui/v2.5/src/docs/en/Manual/Interface.md

@@ -26,6 +26,19 @@ The stash UI can be customised using custom CSS. See [here](https://github.com/s
 
 [Stash Plex Theme](https://github.com/stashapp/stash/wiki/Theme-Plex) is a community created theme inspired by the popular Plex interface.
 
+## Custom Locales
+
+The localisation strings can be customised. The master list of default (en-GB) locale strings can be found [here](https://github.com/stashapp/stash/blob/develop/ui/v2.5/src/locales/en-GB.json). The custom locale format is the same as this json file.
+
+For example, to override the `actions.add_directory` label (which is `Add Directory` by default), you would have the following in the custom locale:
+
+```
+{
+  "actions": {
+    "add_directory": "Some other description"
+  }
+}
+```
 
 ## Custom served folders